Dynamically damped antifriction mounting



M. H MORRIS DYNAMICALLY DAMPED ANTIFRICTION MOUNTING Filed Nov. 14, 1956April 15, 1958 INVENTORQ MARION H. MORRIS 1% 9 7 ATTORNEYS Mum UnitedStates Patent DYNAMICALLY DAMPED ANT IFRICTION MOUNTING Marion H.Morris, Mountain View, Calif., assignor to Sperry-Sun Well SurveyingCompany, Philadelphia, Pa.. a corporation of Delaware ApplicationNovember 14, 1956, Serial No. 622,150 4 Claims. (Cl. 33-223 pendingapplication Serial No. 557,165, filed April 9,, 1956. In these twoapplications there is disclosed a pool of mercury within a sphericalcavity on which there is provided a floating assembly. Due to theparticular construction of the floating assembly as will be hereinafterdescribed in greater detail, the floating assembly is maintainedconstantly centered on the pool of mercury. Thus there is provided anantifriction'mounting of universal angular movement type which issubstantially free of static friction. I

This mounting is so substantially free of friction that, after thefloating assembly has been disturbed and has been set into motion withrespect to the housing, an excessively long period of time is requiredfor the floating assembly to come to rest.

It is the primary object of this invention to provide a damping meansfor the floating assembly.

More particularly, it is the object of this invention to provide, bymeans of a high intensity permanent magnet suspended in the mercurypool, a dynamic damping for the floating assembly.

The foregoing and other objects of this invention, particularly relatingto details of construction, will become apparent from the followingdescription when read in conjunction with the accompanying drawing inwhich the figure is a vertical section showing a floating assemblyincluding a damping magnet in a pool of mercury in association with aninclination and direction indicating means for a well surveyinginstrument.

For the well surveying instrument in general, reference may be made tosaid prior application of Williston and myself and also to the patent ofYoung No. 2,616,187, dated November 4, 1952. Only so much of the wellsurveying instrument is shown in the drawing as is necessary for anunderstanding of the present invention. The other elements not shownherein involve timing means for controlling the time at which one ormore photographic exposures may be made, illumination means, and devicesfor photographing the marked surface of a spherical or other member togive a record from which direction and inclination may be determined.

The inner casing of a well surveying instrument embodying the otherelements mentioned is shown at 2, the casing being receivable within aconventional protective casing sufiiciently strong to withstand the highpressures encountered in bore hole surveying. A pair of housing members4 and 6 are interfitted to provide a spherical cavity 8 presenting asurface non-wettable by mercury, which at its upper end is closed by aglass disc 10 held up 4 V 1C6 in position by ring 12 cemented at 14 andproviding a transparent opening 16. The housing members 4 and 6 arecemented together at 18 and are held in the casing by being pressedagainst a shoulder 20 by means of a threaded ring 22.

A small bore 24 in the housing 6 provides communicatron between thespherical chamber 8 and a fitting 26 threaded into an enlarged bore 25in the housing 6. A valve member 27 having a central bore 27 ispositioned between the end of the fitting 26 and the base of the bore25. The member 27 is formed of a deformable material such as rubber.When the valve member is compressed between the fitting 26 and the baseof the bore 25, the bore 27' in the valve member 27 closes.

The useof the valve member 27 and the filling and evacuation of thechamber 8 forms no part of the present invention and reference may bemade to my prior application Serial No. 557,165 for details involved inthese procedures.

A float'assembly is located within the cavity 8 and comprises ahemispherical body 28 which may be formed of 1 a plastic material suchas nylon. Located under the hemispherical body 28 is a ring 30 ofplastic material having on its exterior cylindrical surface a ribbon ofmetal 32 which in the preferred embodiment of the invention is platinumthough other metals may be used. The assembled ribbon 32 and ring 30 arepressed into a recess provided in the bottom of the body 28 and heldtherein by Nichrome wire pins 34. The inner surface of the ring 30 isconically tapered as indicated at 36.

The float assembly just described is supported by a ool of purifiedmercury 38, the volume of mercury being approximately half the volume ofthe cavity 8, and at any rate being such as to support the float withits spherical surface closely concentric with the spherical surface ofthe cavity 8.

Secured to the underside of the body 28 by pins 40 is a base 42 of apedestal having a stem 44 extending downwardly into the pool of mercury38. A magnet bar 46 forming a compass needle is afiixed to the lower endof stem 44 by means of a screw 48 and is thus positioned within the poolof mercury 38. After the bar 46 is oriented with the North-South markingon the hemispherical body 28, the bar 46, the stem 44 and the screw 48are cemented together as indicated at 50. Desirably, the base 42 and thestem 44 are formed of a non-magnetic material such as aluminumand thecompass bar 46 is an Alnico magnet plated thinly with a silver coating.

As previously noted, the float assembly is supported by the pool ofmercury and a condition of equilibrium exists, maintaining the floatcentrally located, which is apparently due to a considerable extent tothe fact that mercury wets the platinum surface which it contacts anddoes not wet the inner conical surface 36 of the plastic ring. Thus,surface tension action tends to pull the float downwardly into themercury in excess of the degree of immersion which would result solelyfrom the weight of the float. Under these conditions, equilibrium isattained only when the float is centrally located. Any tendency to movetransversely results in an elevation of the center of gravity of thesystem by displacement of mercury, and hence reliable return to thecentral equilibrium position is assured. By reason of thenon-contamination of the mercury surface, there is furthermore produced,to the extent to which observation may be made, a complete absence ofstatic friction. In other words, in response to a magnetic field, thefloat will assume an azimuthal position to an extremely high degree ofaccuracy.

The conditions involved in the maintenance of this condition ofequilibrium are more fully set forth in the 3 above mentionedapplication of Samuel H. Williston and myself, Serial No. $51,024.

It should be noted that the weight of the floating assembly is adjustedso that the upper edge 31 of the mercury meniscus adjacent to theplatinum ribbon 32 is positioned below the bottom of the nylon body 28.Thus, the meniscus is freeto seek its own level against the platinumribbon without interference from the nylon body.

It will be evident when the compass needle 46 is displaced from aNorth-South position, the earth's magnetic forces will cause it to seeka North-South position. Due to the low friction of the mounting and theinertia of the float, there is a tendency for the floating assembly tooscillate. Tilting oscillations also occur about the position ofequilibrium. f

However, by employing a high intensity magnet such as an Alnico magnetand positioning the magnet in the mercury pool 38 as shown, movement ofthe magnet within the pool generates eddy current in the mercury.

This generation of eddy currents dissipates the inertial energy of thefloat assembly and thus provides a true dynamic braking. The effect ofthe structure is to provide a highly damped and extremely low frictionmounting.

It will be noted that the hemispherical body 28 is solid and thus if thebody is caused to assume the position rotated on a horizontal axis 90from that shown in the drawing the pool of mercury will apply force notonly downwardly against the inner surface 36 of the ring 30 but alsohorizontally against the lower half of the under surface of the body 28.The force of this mercury acting against the body 28 will cause the bodyto rotate and to assume a floating position such as that shown in thedrawing. Were the hemispherical body hollow this would not occur due tothe fact that the pressure of the mercury would be acting downwardlyover a major portion of the surface of the body with which it would bein contact and it would thus press the body against the inner wall ofthe spherical cavity 8 with such force as to prevent its rotating andassuming a floating position. Thus, in handlingor when undergoing rapidmovement, the float assembly always aligns itself promptly in a floatingposition. This construction in combination with the magnetic dampingprovides a reliable and highly damped extremely low friction mountingfor a magnetic compass or other floating.

apparatus.

While the invention has been described herein as emeluding a magnetizedmember submerged in said pool of mercury providing dynamic damping ofmovement of said floating means on said pool of mercury.

2. Apparatus comprising a pool of mercury, means floating on said poolof mercury and freely rotatable thereon, said floating means including amagnetized member submerged in said pool of mercury providing dynamicdamping of rotary movement of said floating means on said pool ofmercury.

3. An antifriction mounting comprising a container presenting a surfacenon-wettable by mercury, a pool of mercury in said container, and afloat assembly in said pool .of mercury presenting to the surface of themercury a solid surface having characteristics such that at a line ofcontact the mercury has a meniscus that is concave upwardly and saidfloat assembly including magnetized member submerged in said pool ofmercury providing dynamic damping of movement of said floating means onsaid pool of mercury.

4. Antifriction mounting comprising a container presenting a surfacenon-wettable by mercury, a pool of mercury in said container and a floatassembly in said pool of mercury presenting to the surface of themercury a solid surface having characteristics such that at a line ofcontact the mercury has a meniscus that is concave upwardly and saidfloat assembly including a rotatable magnetized member submerged in saidpool-of mercury providing dynamic damping of movement of said floating vmeans on said pool of mercury.

References Cited in the file of this patent UNITED STATES PATENTS1,294,710 Roland Feb. 18, 1919 1,397,490 Peradotto Nov. 15, 19211,912,358 Bush June 6, 1933 2,765,541 Story Oct. 9, 1956

